Electron beam tube having a collector electrode insulatively supported by a cooling chamber



June 1968 M. MARIE-CLEMENT ARNAUD 3,333,281

ELECTRON BEAM TUBE HAVING A COLLECTOR ELECTRODE INSULATIVELY SUPPORTED BY A COOLING CHAMBER Filed Aug. 5, 1965 3 Sheets-Sheet 1 Imam 8 June 1968 M. MARIE-CLEMENT ARNAUD 3,333,281

ELECTRON BEAM TUBE HAVING A COLLECTOR ELECTRODE I INSULATIVELY SUPPORTED BY A COOLING CHAMBER Filed Aug. 5, 1965 3 Sheets-Sheet 2 J1me 1968 M. MARIE-CLEMENT ARNAUD 3,

ELECTRON BEAM TUBE HAVING A COLLECTOR ELECTRODE INSULATIVELY SUPPORTED BY A COOLING CHAMBER Filed Aug. 5, 1965 5 Sheets-Sheet 3 United States Patent 1 8 Clanns. (Cl. 315-3.5)

ABSTRACT OF THE DESCLOSURE This invention discloses a high-frequency power electron tube operating with a beam of electrons and comprising a collector to which a depressed voltage may be applied. In this tube, an apertured diaphragm electrode, which is at the potential of the HF circuit component of the tube, is located between the collector electrode and HF circuit component and extends longitudinally between the two transverse front-walls of a double-walled all-metal cooling-jacket in the shape of a cylindrical box which extends to the rear-end of the tube and surrounds the collector electrode. A cooling liquid circulates in the jacket and not only cools the diaphragm electrode which is accessible to said liquid but cools also the collector electrode by dissipating the heat radiated from the collector to the jacket.

The present invention relates to electron tubes in which a high frequency voltage is produced or amplified by means of an electron beam which passes through an energy exchange arrangement hereinafter referred to as HF circuit, the beam being subsequently caught by a collector or target electrode which does not itself participate in the HF energy exchange.

The most usual types of tube are klystrons and wave propagating tubes, but triodes and tetrodes have also been constructed on the same principle. The invention discloses improvements in these tubes and in the amplifiers or generators in which they are incorporated which enables a method known per se to be exploited to particular advantage, the method consisting in applying to the target electrode a potential which is lower than the DC. potential of the HF circuit.

It is a well-known fact that in these beam tubes such as klystrons and wave propagating tubes, the electron beam passes through the tube at a certain speed and gives 0 up a portion of its kinetic energy to a HF circuit where it is converted into HF power. Electrons leaving the region of the tube in which the HF circuit is located still have a considerable velocity and if they reach a target electrode which is brought to the same potential as the elements of the HF circuit, this energy is simply converted into heat. This results in a low output from the tube and heating of the target electrode.

For some time, attempts have been made to increase the efficiency of these tubes by reducing the speed of the beam after it leaves the vicinity of the HF circuit. It has, in fact, been attempted to apply to the target electrode a potential which is lower than that of the HF circuit components but this method raises the following problems:

(1) It is necessary to avoid the return of the electrons to the components of the HF circuit, whether these are electrons which have been reflected in the retarding field or secondary electrons which have been released from the surface of the target electrode. In fact, the return of electrons in this manner risks reducing the efficiency of the HF circuit and even destroying those components of the HF circuit which are not easily able to dissipate heat.

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(2) It is necessary to avoid the retarding field extending as far as the HF circuit, since this would result in premature deflection of the primary beam and would also result in components of the HF circuit intercepting the current.

(3) It is necessary to have very good insulation between the target electrode and the components of the HF circuit, which are generally earthed. This raises a number of serious problems, particularly if the target electrode comprises a cooling arange'rnent in which there circulates a coolant fluid, in which case it is necessary for the whole arrangement to be insulated with respect to earth.

A number of solutions have already been put forward to avoid undesired electrons reaching the components of the HF circuit, either by reducing the production of secondary electrons at source, eg choice of material, shape and state of the surface of the target electrode, or by forming traps using electrostatic or magnetic arrangements which compel the electrons leaving the target electrode to return to it. However the devices which make use of these principles are not entirely satisfactory. Some arrangements only allow the potential of the target electrode to be slightly reduced. When the reduction is greater their HF circuit receives a considerable current, either as a result of returning electrons or of electrons from the primary beam which have diverged prematurely. The conventional devices which permit a substantial reduction in the potential of the target electrode are complicated for example, they make use of a series of elementary collectors which have been brought to different potentials. No solution has so far been put forward with regard to the problem of insulation, when cooling is effected by means of a liquid.

One of the main objects of the invention is to produce an electron beam tube in which the target electrode may be brought to a potential very much below that of the preceding components very simple means being used to obviate the disadvantages and difficulties referred to above.

Another object of the invention is to produce a high frequency oscillation amplifier or generator which incorporates an improved tube of this type and with an arrangement which enables full use to be made of its advantages.

The invention relates to an electron beam tube comprising at least one sealed envelope, a cathode, an accelerating electrode or anode, a high frequency circuit which is able to generate or amplify a high frequency voltage by interaction with the electron beam, and a target electrode in which the end portion of the sealed envelope containing the target electrode is constituted by a chamber with a sealed metal enclosure, herein referred to as the end chamber, composed of transverse portions and a longitudinal portion, with respect to the axis of the tube and comprising:

A metal jacket enclosing at least the longitudinal part of the enclosure of the end chamber and connected thereto so as to form, with the enclosure, a closed space, conduits being introduced into the jacket in order to allow a liquid to circulate within the closed space,

A diaphragm electrode forming part of the enclosure at the side facing towards the cathode and having an aperture to allow the beam to pass through and being located near the closed space so as to be accessible to a liquid which circulates within the enclosed space,

A sealed insulated passage for the electrical supply line to the target electrode,

Means for supporting the target electrode at a distance from the enclosure while maintaining electrical insulation with respect to the enclosure.

To simplify the arrangement, the target electrode may be held in place by one or more fixed rods which pass through the insulating passage or passages in the end chamber.

In those tubes which require a magnetic field to guide the beam through the HF circuit, the field is advantageously located as far as possible from the inside of the end chamber. This may be done, for instance, by making either the diaphragm electrode or at least part of the jacket of a ferromagnetic material, if this part extends on the wall of the chamber at the side adjacent the cathode.

In an advantageous embodiment, the aperture in the diaphragm electrode is flared out in the direction of the target electrode and is followed, on the side adjacent the cathode by a channel allowing passage to the beam, the target electrode having a concave surface facing the diaphragm electrode, for example a hollow cone in the solid beam tubes.

The features mentioned above may be applied both to solid beam tubes, which are usually of circular section, and to hollow beam tubes, which are usually of annular section. In the former case the diaphragm electrode is a plate with a central aperture while in the latter case it is formed by two coaxial annular plates defining an annular aperture.

In order to enable the advantages of this improved tube to be exploited, the HF oscillation amplifiers or generators which incorporate the tube must permit the accelerating electrode, the high frequency circuit and the end chamber to be brought to the same potential, which is positive with respect to the cathode and the target electrode to be brought to a potential which is lower than the former. When the tubes used require a magnetic field to guide the beam and have either a diaphragm electrode or the jacket of the end chamber turned towards the cathode made of ferromagnetic material, the means for producing the magnetic field are preferably surrounded by a ferromagnetic screen connected with slight reluctance to the ferromagnetic element in the chamber.

In the tube according to the invention, the electronic beam passes through the diaphragm electrode and is then retarded as it approaches the target or collector electrode which is at a relatively low potential. In the course of the retarding process it diverges under the influence of its space charge and because of the absence of any electrostatic or magnetic concentrating means. In fact, the magnetic focusing field, which may be applied to the preceding path of the beam, is kept away from the inside of the end chamber by means of the magnetic screen which is constituted either by a portion of the jacket which is turned towards the cathode or by the diaphragm electrode, one or other of which is made from ferromagnetic material and magnetically connected with a sufliciently low reluctance to a casing outside the means generating the field, which means may be a solenoid. The residual field may then be reduced or removed by means of a compensating coil surrounding the end chamber. In this way the area of impact of the electrons on the target is much larger than the cross-section of the aperture in the diaphragm. The electrons which are not caught by the target because of their low velocity and the secondary electrons released from its surface by rapid primary electrons move towards the diaphragm and are there caught on a surface which is also much greater than the inlet aperture in the diaphragm. Since moreover the beam inlet channel may without disadvantage have a cross-section which is very little larger than that of the beam and a length which is a multiple of its own width, it is extremely improbable that electrons will return via the channel to the high frequency circuit. It should be noted that the diaphragm electrode, which may be extended by an inlet channel, forms an electrostatic screen which effectively protects the components of the high frequency circuit from the retarding field between the electrode and the target.

Because the diaphragm electrode and the beam passage channel are cooled by means of a liquid, they are able to withstand the bombardment of returning electrons. The device which effects this cooling is at the potential of the HF circuit and may therefore be earthed, thus avoiding any insulation problems. Then again the target has a very slight thermal load since the diaphragm effectively catches the returning electrons and the target may be at a very low potential. The target is consequently cooled sufiiciently according to the invention by its thermal radiation which is directed towards the wall by which it is enclosed at a distance and which is cooled by the circulation of a liquid. The invention thus achieves its object of effectively preventing the return of electrons to the high frequency circuit, even when the potential of the target is extremely low, this object being, moreover, attained in the case of a tube which is designed so as to avoid any difiiculty with regard to the electrical insulation of a liquid cooling arrangement.

The invention will now be further described by way of example with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view of a full beam wave propagating tube incorporating the improvements of the invention and completed by external members so as to constitute a microwave amplifier arrangement which enables the improvements to be fully exploited,

FIGURE 2 is a diagrammatic view of the end portion of a hollow beam wave propagating tube incorporating the improvements of the invention, and

FIGURE 3 is a graph showing the extensive possibilities of reducing the potential of the target electrode with respect to that of the HF circuit in a tube according to the invention.

The travelling wave tube according to FIGURE 1 is shown with a break through the centre of the tube since the tube is relatively long and could not be shown in its entirety on a sufliciently large scale to show the important features of the invention.

The tube comprises the following three parts:

An assembly 4 containing an electron gun, a centre portion containing, within a metal enevolpe 1, the high frequency circuit through which there passes the electron beam, and an end chamber 5 containing a target electrode. The assemblies 4 and 5 are connected in a sealed manner to the envelope 1 0f the central portion by means of plates 2 and 3 which are of ferromagnetic material and provided with a central aperture.

The assembly 4 comprises an electron gun formed by a cathode 9, a concentrating electrode 11 and an accelerating electrode or anode 12. These components are enclosed in a sleeve 13 of ceramic material, one end of which is secured to a cover 14 while the other end is secured to the cylindrical edge of the anode 12. The cover 14 supports the passages for the cathode conductors, its heating filament and its focusing electrode together with an evacuation tube. Only the passage 15 for the cathode connection has been shown of these in the figure since all these components are of conventional design and are not directly related to the present invention. For the same reason the cathode heating filament has not been shown. The anode is formed by a tubular element which passes through a plate 12 and forms on the plate a first projection 16 facing the cathode 9 and a second projection 16a which is turned towards the tube 1. The central aperture of the anode flared out towards the cathode and the projection 16, are shaped in a conventional manner so as to concentrate the electrons emitted by the cathode into a beam of circular section which passes along the axis of the tube. The anode is secured, by means of its second projection 16a and by the outside edge of its plate 12, to the ferromagnetic plate 2. The plate 2 and the plate 12 are thus located a small distance apart and define a space 17 which may be traversed by a coolant fluid which is conveyed through a conduit 18 and which leaves the arrangement through another conduit not shown in the figure.

The central portion of the tube, which is enclosed in the metal envelope 1 has a HF circuit composed of a delay line 6 which is helical in form and extends over almost the whole length of the envelope 1 with its ends secured to sealed, insulating passages 7 and 8, to which are connected the coaxial lines 7a and 8a which respectively convey the signal to be amplified and the amplified signal..

The end chamber is constituted by a metal box formed by internal and external walls 22 and 22a respectively, the portion of the external wall 22a which faces the cathode 9 being formed by the ferromagnetic plate 3. The portion of the internal wall 22 adjacent the plate 3 is constituted by a copper diaphragm electrode 19 in the form of a plate and traversed by a tubular element which forms a first projecting portion 21 turned towards the inside of the chamber and a second projection 21a turned towards the ferromagnetic plate 3. The projection 21a is welded in the central aperture of the plate 3. The projections 21 and 21a are very similar to the projections 16 and 16a of the anode 12. The hollow part of the electrode 19 is equal in length to a multiple of its axial length and is flared outwards towards the inside of the chamber. Furthermore, the external diameter of the electrode 19 is a multiple of that of the central aperture of the projection 21a. The wall 22 of the chamber encloses with clearance a collector of target electrode 26 made of refractory material and having a surface with a. high radiation coefiicient. Both conditions are fulfilled if, for example, the electrode is made of a substance such as graphite. This electrode has at its side turned towards the electrode 19 a concave surface which in the example shown is a hollow cone. It is held in place at the opposite side by means of a rod 23, which may be of molybdenum, which passes through the far end of the chamber via a sealed, insulating passage formed by a ceramic tube 24. Conduits and 26, which pass through the outer wall 22a, allow a coolant liquid to circulate in the space enclosed between the walls 22 and 22a.

The central portion of the tube is surrounded by a magnetic focuscing coil 29 which is able to produce a magnetic field along the axis of the helical delay line 6. This magnetic field is closed by the ferromagnetic plates 2 and 3 and a screen 39, also of ferromagnetic material, the end portions of which magnetically reconnect the plates 2 and 3. They may also be separated from these plates by means of slots or gaps with a low reluctance. Where there is no contact between the casing and the plates 2 and 3, it is advisable for safety reasons to provide an electrical connection between the casing 39 and the metal envelope of the tube, since this allows almost all the components which are accessible from the amplifier to be earthed. Outside the space defined by the ferromagnetic elements 2, 3 and 30, the end portions of the tube are again enclosed by auxiliary coils 31 and 32a. These coils are traversed by a current of opposite sense to that of the coil 29 and enable the residual field of this coil, which is outside the space limited by the plates 2 and 3, to be reduced.

The cathode 9 of the tube is connected to the negative terminal of a voltage source, diagrammatically represented by a battery E. The positive terminal of this source is connected to the metal enclosure of the chamber 5 and is thus connected to the anode 12, the helical delay line 6 and to the annular electrode 19. An intermediate terminal of the battery E is connected to the rod 23 supporting the target 20. Certain additional components which are not necessary for understanding the figure, such as switches, supply lines for the coils 30, 31, 31a and for the cathode filament are not shown in the figure.

In the operation of the device shown in FIGURE 1, electrons 27 emitted by the cathode 9 are concentrated and accelerated by the electrodes 11 and 12 so as to form a narrow beam 28 which travels along the axis of the tube 1. As the beam 28 passes through the tube 11, the beam keeps its shape under the efiect of the magnetic field produced by the coil 29. As the beam passes along the axis of the tube 1, the beam 28 passes through the delay line 6. The latter enables a decelerated HF wave to be propagated in such a manner that the phase velocity of the HF wave is approximately equal to the velocity of the beam. The electrons bunch together and transmit a portion of their energy to the wave which is travelling along the helical delay line 6. The HF wave is fed into the coaxial line 7a and may be collected after amplification through the coaxial line 8a.

At the output of the delay line 6, the beam still possesses considerable kinetic energy. After passing through the diaphragm 19, it enters a retarding field, since the target 20 has been brought to a potential which is lower than that of the electrode 19. Owing to the fact that its central aperture is relatively small, the latter electrode forms a very eifecive electrostatic screen which protects the interaction space containing the delay line 6 from the retarding field. There is little or no focusing magnetic field in the retarding area because of the provision of the ferromagnetic plate 3 and the auxiliary coil 31a. The electrons are thus dispersed within this space, under the elfect of the space charge, in directions such as 32, their dispersion being further encouraged by the concave shape of the surface of the target turned towards the electrode 19. The beam begins to diverge in the splayed out part of the aperture in the electrode 19. The electrons which because of their low velocity are not caught by the target, return to the electrode 19 along paths such as those indicated by dotted arrows 32a and are caught by the electrode 19. The secondary electrons which have been released from the surface of the target by electrons moving more rapidly than the beam and which leave the surface of the electrode in a number of different directions are spread over the surface of the electrode 19 and the wall of its central aperture and are thus also caught. It is extremely improbable that either type of electron should escape through the narrow aperture in the electrode 19 and return to the HF interaction space.

The heat produced by the captured electrons on the target is reflected towards the walls of the chamber 5 and is dissipated by liquid circulating between the walls 22 and 22a. The same liquid also dissipates the heat which is generally greaterproduced by the electronic bombardment of the electrode 19. It is clear that the problem of cooling the two electrodes is solved using only one liquid circulating device which may be brought to the same potentital as earth.

FIGURE 2 is a partial View which only shows the end portion and a part of the delay line of a travelling wave tube according to the invention but of a different kind from that shown in FIGURE 1. The tube shown in FIG- URE 2 differs from that shown in FIGURE 1 in that it makes use of a hollow electron beam 33. The beam passes through a delay line in the form of a helical coil 34 located within a tubular metal envelope 35 and secured in place by three ceramic rods 36. The rods 36 are secured by their ends to a metal disc 37. The end of the delay line 34 is connected to a coaxial output line 38 closed at both ends by a sealed securing means 62 and 63.

The end chamber is in the form of an annular construction comprising three coaxial compartments, viz. a central cylindrical compartment 39 cooled by means of a fluid conveyed through the conduits 4t) and 41, an intermediate annular oompantment 48 containing an annular target 42 and an external annular compartment 43 cooled by means of a fluid conveyed through the conduit 44 and through another conduit not shown in the figure. It can be seen from FIGURE 2 that the outer envelope 45 of the compartment 43 is secured to the end of the tubular envelope 35. The envelope 45 forms a jacket which defines together with the other pieces of the chamber a closed space which is traversed by a circulating liquid. At its lower part this jacket 45 is welded to two annular discs 46, 47 which support the other parts which form the end chamber of the tube. Moreover the disc 46 adjacent the tube 35 serves, by means of the piece 37, to secure the supports for the helix 36 while the disc 47 forms part of the base of the tube. The discs 46 and 47 are traversed by the coaxial output line 38 and the disc 47 is also traversed by the conduit 44 for the coolant fluid and by the other conduit which is not shown in the figure.

The intermediate annular compartment is defined by a cylindrical outer wall 64 secured to the disc 47 and by a cylindrical inner wall 49 held in place by an annular base 50. Three rods such as the rod 51, which support the target 42, pass through the base 50 by means of scaled, insulating passages such as 52. At its end located adjacent the beam 33, the intermediate annular compartment is partly closed by rings of ferromagnetic material 53 and 54, which are secured to the edges of the walls 48 and 49 respectively. The rings 53 and 54 form a diaphragm with an annular aperture through which the hollow electron beam 33 passes. The annular aperture is extended in the direction opposite the direction in which the beam moves by two revolving portions 56 and 57. The portion 56 is a section of tube with one end secured to the ring 53 and the other end fixed to the disc 46, while the portion 57 is a cap with its edges secured to the ring 54. The cap 57 thus closes one end of the central chamber 39. The other end of the chamber 39 is closed by a stopper 58 which supports the conduits for the coolant fluid 4t 41.

The end chamber of the tube passes through the aperture of a plate 59 of ferromagnetic material which is located at the height of the ferromagnetic rings 53 and 54. The assembly 53, 54 form the rear portion of a magnetic screen which serves to limit the field of a focusing solenoid surrounding the tubular envelope 35 which is not shown in the figure. It should be noted that the gaps between these three elements have a very low reluctance. In the figure the thickness of the compartment 43 has been shown on an enlarged scale for the sake of clarity.

The arrangement of the components in FIGURE 2 shows characteristics of operation which are similar to those of the travelling wave tube as shown in FIGURE 1. After passing through the diaphragm electrode 53, 54, the electrons of the annular beam 33 leave the magnetic focusing field and are subjected to the electrical retarding field produced by the annular target 42 which is at a potential very much below that of the rings 53, 54. They then disperse along paths such as 60. The electrons which are not caught by the target and the secondary electrons freed therefrom return to the rings 53 and 54 which thus act as a screen in the same manner as does the electrode 19 of the tube shown in FIGURE 1. The rings 53 and 54 are cooled by the coolant fluid which circulates in the chamber 39 and 43 and the walls 64 and 49 thus cooled enable the heat reflected from the target 42 to be dissipated. As in the previous embodiment, the target 42 is made of a refractory material such as graphite and the part of its surface turned towards the beam is hollowed out. In order to limit the heat radiation from the target to the cooled area of the walls 48 and 49, a number of annular discs such as 61 of thin metal have been mounted behind the target 42 on the supporting rods 51.

The above description shows how in the tubes according to the invention it is possible to bring the collector or target electrode to a potential which is very much below that of the HF circuit, without thereby raising difficulties with regard to the cooling of the target and the screen electrode. The advantage obtained by lowering the potential U of the target with respect to the cathode will be explained with reference to FIGURE 3 which shows a graph obtained experimentally with a tube of the type shown in FIGURE 1 and showing, as a function of the ratio OC U /U (where U, represents the potential common to the diaphragm, the HF circuit and the ac- It should be noted that the nominator of the latter fraction expresses the power which is dissipated in a tube which does not permit the potential of the collector electrode to be reduced below that of the HF circuit.

The graph shown in FIGURE 3 shows that if the voltage of the target is twelve times lower than that of the HF circuits, the total power lost in the target and the diaphragm is reduced to one quarter.

I claim:

1. Electron beam tube comprising a sealed envelope, including a cathode and an accelerating electrode for forming and projecting an electron beam within the envelope, in coupling relation with a high frequency circuit which is able to modify a high frequency voltage by interaction with the electron beam, and a collector electrode contained within the end portion of the sealed envelope remote from said cathode, said end portion comprising a liquid cooled chamber, and

spaced transverse metal wall portions and a longitudinal metal wall portion defining said chamber,

a metal jacket enclosing at least the longitudinal wall portion of the chamber and so connected as to form,

a closed space between said jacket and chamber, conduits connected to the jacket in order to allow a liquid to circulate within the closed space,

a diaphragm electrode secured to and forming at least part of one of said transverse wall portions and positioned between said collector electrode and cathode, said diaphragm electrode having an aperture to allow the electron beam to pass through and be cooled by a liquid which circulates within the closed space,

an electrical supply line to the collector electrode insulated from the metal walls of the chamber, and

means for supporting the collector electrode spaced from the metal walls of the chamber while main- I taining electrical insulation with respect to the metal walls of the chamber.

2. An electron beam tube as claimed in claim 1, wherein the collector electrode is insulatingly supported from the metal walls of the chamber by said supply line.

3. An electron beam tube as claimed in claim 1 wherein the aperture in the diaphragm electrode which admits the beam is flared outwards in the direction of the collector electrode and the surface of this electrode turned towards the aperture has a concave portion.

4. An electron beam tube as claimed in claim 1, wherein the diaphragm electrode is made of ferromagnetic material.

5. A high frequency amplifier incorporating an electron beam tube as claimed in claim 4, wherein voltage sources are provided to bring the accelerating electrode, the high frequency circuit and the chamber of the tube to a potential which is positive with respect to the cathode and the collector electrode to a potential between that of the cathode and that of the high frequency circuit, while magnetic means produce a magnetic focusing field which focuses the electron beam, a ferromagnetic shield enclosing the magnetic means and connected magnetically by a low reluctance bond with the portions of ferromagnetic material in the transverse portion of the chamber which faces towards the cathode.

6. An electron beam tube as claimed in claim 1 wherein a portion of the jacket extends at least partly over the transverse wall portion of the chamber comprising said diaphragm electrode and is made of ferromagnetic material.

7. A high frequency amplifier incorporating an electron beam tube as claimed in claim 6, wherein voltage sources are provided to bring the accelerating electrode, the high frequency circuit and the end chamber of the tube to a potential which is positive with respect to the cathode and the collector electrode to a potential between that of the cathode and that of the high frequency circuit, which magnetic means produce a magnetic focusing field which focuses the electron beam, a ferromagnetic shield enclosing the magnetic means and connected magnetically by a low reluctance bond with the portions of ferromagnetic material in the transverse portion of the chamber which faces towards the cathode.

8. A high frequency amplifier incorporating an electron beam tube as claimed in claim 1, wherein voltage sources are provided to bring the accelerating electrode, the high frequency circuit and the chamber of the tube to a potential which is positive with respect to the cathode and the collector electrode to a potential between that of' the cathode and that of the high frequency circuit.

References Cited UNITED STATES PATENTS 2,515,997 7/1950 Haetf 3155.38 2,867,747 1/1959 Murdock 31339 X 2,949,558 8/1960 Kompfner et a1. 313-5.38 X 2,955,225 10/1960 Sterzer 3153.5 2,958,804- 11/1960 Badger et al. 3153.5 X 3,172,004 3/1965 Von Gutfeld et al. 315-3.5 X 3,188,515 6/1965 Kompfner 315-35 HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, JR., Assistant Examiner. 

